Curved throat scan horn for the transmission of electromagnetic energy



Oct. 18, 1955 R. C. SPENCER CURVED THROAT SCAN HORN FOR THE TRANSMISSION OF ELECTROMAGNETIC ENERGY Filed NOV. 13, 1945 FIG.2

FIG.3

INVENTOR ROY CLARENCE SPENCER ATTORNEY United States Patent CURVED THRUAT SQAN HGRN FOR THE TRANS- MISSION OF ELECTRGMAGNETIC ENERGY Roy C. Spencer, Arlington, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application November 13, 1945, Serial No. 628,283

17 Claims. (Cl. 25033.63)

This invention relates to directionalmicrowave antenna systems adapted to produce a rapidly reciprocating or scanning sharp beam of radiation, and relates more par ticularly to a type of construction of a horn feed for a reflector, said horn being characterized by a curved throat so that energy may be fed into the horn throat from the open end of a wave guide moving in a circular path and thereby produce the same result as if the wave guide were moved linearly back and forth-across the throat opening of a flat tapered horn. If the output of such a horn is directed against a parabolic cylindrical reflector there results a plane wave which will vary in direction at the frequency at which the wave guide feed is mechanically oscillating. The rapidity of the scanning rate imposes dilficulties in feeding a flat horn throat with a reciprocating movement of the guide feed.

It is the object of this invention to construct a tapered horn for feeding a parabolic reflector with an energy beam of varying directivity, and adapted to be fed from a single open ended wave guide moving in a circular path.

- It is another object to construct a tapered horn feed which may be energized by a single open ended wave guide moving in a circular path for producing a variably directed energy beam at the output end of said horn suitable for illuminating any reflector adapted to produce therefrom a plane wave front, whereby 'a scanning directional beam may be obtained.

An object of this invention may also be described as providing a tapered horn which maybe excited by an open end wave guide travelling in a circular are at its throat to produce the same effect as a flat tapered horn excited at its throat by a linearly transversely reciprocating wave guide end.

Another object is to construct a curved throat horn which can be manufactured from plane metal sheets by cutting and bending only. 7

It is also an object of this invention to construct a horn for producing in effect a straight line source which radiates a beam the direction of which varies corresponding to the position of a feed which moves around a circular path at the throat of the horn.

Other objects and features will become apparent from consideration of the following detailed description taken together with the drawings, the figures of which are to be deemed as illustrative and not to limit the invention as otherwise disclosed and claimed.

Fig. 1 shows a parabolic cylindrical reflector included between two parallel conductive plates and a movable feed for the reflector which moves transversely back and forth to cause periodic scanning of the pattern of radiation from the reflector;

Fig. 2 shows an application of this type of scanning feed;

Fig. 3 shows the lines along which the flat faces of a horn may be cut and rolled up cylindrically so that the throat or opening into the horn approximates a semicircle; and

i Fig. 4 shows in perspective a type of scanner using the semi-circular throat.

Referring now to Fig. 1, there is shown a pair of parallel plates 1 and 3 and a parabolic cylindrical plate 5 included between them. In the aperture of the parabola is a laterally movable wave guide horn feed 7 which may be moved to left and right between the plates 1 and 3. When the feed 7 is in the middle, or at the focus, the beam from the reflector will be directed back in the direction of the axis 11 of the reflector. As the feed is moved laterally to either side the beam will radiate correspondingly to a direction, as 13 or 15 differing from the axial direction.

Fig. 2 shows a scanning antenna using a laterally movable wave guide feed. Included is a pair of substantially parallel plates 21 and 23 of flared or trapezoidal shape fed at the small end by a Wave guide horn 25 which can be reciprocated back and forth across the smaller end 27 as indicated by the arrows 29 and 31. This transverse motion of the feed 25 will cause a changing of the direction. of output from the larger end. This output may be reflected from a portion of a conical reflector 33 to produce a plane wave front beam 35 at right angles to the axial direction which changes in direction according to the movement of the feed 25.

Such laterally reciprocating motion of a feed, especially for rapid scanning, involves mechanical difficulties. The same result may be obtained from a rotary or revolving motion of a feed by rolling up the two parallel plates in the region of the throat of the horn in a cylindrical manner with the dotted lines 41, 42, 43, 44 etc. of Fig. 3 as cylindrical elements so that the feed path approximates a semi-circle, as shown in Fig. 4.

In Fig. 4 are shown two tapered plates 51 and 53 rolled cylindrically at the throat end into a semi-circular opening leaving the wider end flat. An open ended wave guide or feed horn 55 is represented which can be caused to move back and forth along the throat aperture in a circular arc, or preferably caused to traverse the throat opening by a rotary motion (by means not shown). There will result effectively a line source at the wide end 57 of the rolled horn which will vary its apparent orientation as the feed 55 varies in its position. This line source can be used to illuminate a reflector 59 and thereby produce a rapid scan fanned beam of radiation. In the figure a reverse bend 58 has been made in the horn merely to reverse the direction of propagation. The principle of this invention, namely the rolling of the flat plates into a circular arc throat entrance aperture while retaining the mouth of the horn or a long narrow rectangular aperture as an effective line source, can be carried to a further application by forming the throat into a full circle so that there results a full rolled throat horn (not shown) comprising two adjacent parallel plates with one pair of adjacent edges rectilinear and parallel, and the opposite pair of adjacent edges formed essentially into two complete concentric circles.

I claim:

- 1. In an antenna, a horn having a pair of substantially parallel conductive surfaces having one pair of adjacent edges formed into two concentric circular arcs bounding an annular opening, having the pair of edges opposite thereto forming a narrow rectangular opening, and a source of electromagnetic energy adapted to repeatedly traverse said annular opening.

2. In an antenna, a scanning horn having a pair of substantially parallel conductive surfaces having one pair of adjacent edges formed into two concentric circular arcs, and having a second pair of edges opposite said first pair straight and parallel bounding a narrow rectangular opening, and a source of electromagnetic energy adapted to be revolved so as to repeatedly traverse lengthwise said circular opening.

3. A horn antenna for radiating electromagnetic energy comprising, a pair of uniformly spaced conductive surfaces, each surface having a corresponding edge rolled into a predetermined curve thereby forming a curved throat aperture. I

4. A horn antenna for radiating electromagnetic energy comprising, a pair of uniformly spaced conductive surfaces, each surface having a corresponding edge rolled into a circular are thereby forming a cylindrical throat aperture.

5. A tapered horn antenna for producing a variably directed electromagnetic energy beam comprising, a pair of uniformly spaced conductive surfaces, each surface having a corresponding edge rolled into a predetermined curve thereby forming a curved throat aperture, means to feed electromagnetic energy to said horn and means to cause said feed means to traverse said throat aperture.

6. A tapered horn antenna for producing a variably directed electromagnetic energy beam comprising, a pair of uniformly spaced conductive surfaces, each surface having a corresponding edge rolled into a circular are thereby forming a cylindrical throat aperture, means to feed electromagnetic energy to said horn and means to cause said feed means to traverse said throat aperture.

7. A tapered horn antenna for producing a variably directed electromagnetic energy beam comprising, a pair of uniformly spaced conductive surfaces, each surface having a corresponding edge rolled into a circular are thereby forming a cylindrical throat aperture, an open ended waveguide feed for electromagnetic energy and means to cause said Wave guide feed to traverse said throat aperture by rotary motion.

8. A tapered horn antenna for producing a variably directed electromagnetic energy beam comprising, a pair of conductive surfaces of the same shape, one of said surfaces being superimposed over the other of said surfaces and uniformly spaced therefrom, each of said surfaces having a first edge rolled into a circular arc to form a cylindrical throat aperture and a second linear edge opposite said first edge to form a long narrow rectangular aperture, each of said first edges having a perimetric length substantially shorter than the linear length of each of said second edges.

9. A tapered horn antenna for producing a variably directed electromagnetic energy beam comprising, a pair of conductive surfaces of the same shape, one of said surfaces being superimposed over the other of said surfaces and uniformly spaced therefrom, each of said surfaces having a first edge rolled into a circular arc to form a cylindrical throat aperture and a second linear edge opposite said first edge to form a long narrow rectangular aperture, each of said first edges having a perimetric length substantially shorter than the linear length of each of said second edges, said second edges defining a parabolic reflecting surface having its focus at the mid point of said cylindrical throat.

10. A tapered horn antenna for producing a variably directed electromagnetic energy beam comprising, a pair of conductive surfaces of the same shape, one of said surfaces being superimposed over the other of said surfaces and uniformly spaced therefrom, each of said surfaces having a first edge rolled into a circular arc to form a cylindrical throat aperture, a second linear edge opposite said first edge to form a long narrow rectangular aperture, each of said first edges having a perimetric length substantially shorter than the linear length of each of said second edges, said second edges defining a parabolic reflecting surface having its focus at the mid point of said cylindrical throat, an open ended wave guide feed for electromagnetic energy and means to cause said Wave guide feed to traverse said throat aperture by rotary motion whereby a plane wave front beam of electromagnetic energy is radiated with a directivity corresponding to position of said feed as it traverses said throat.

ll. A tapered horn antenna for producing a variably directed electromagnetic energy beam comprising, a pair of conductive surfaces of the same shape, one of said surfaces being superimposed over the other of said surfaces and uniformly spaced therefrom, each of said surfaces having a first edge rolled into a circular arc to form a cylindrical throat aperture and a second straight edge opposite said first edge to form a long narrow rectangular aperture, each of said first edges having a perimetric length substantially shorter than the linear length of each of said second edges, said second edges defining a conical parabolic reflecting surface to produce a changed direction of propagation of electromagnetic energy, an open ended wave guide feed for electromagnetic energy and means to cause said Wave guide feed to traverse said throat aperture by rotary motion whereby a beam of electromagnetic energy is radiated with a directivity corresponding to position of said feed as it traverses said throat.

12. Apparatus of claim 11 wherein the surfaces at said linear edges are further extended and bent so as to form a reverse bend for reversing the direction of propagation through said horn.

13. In an antenna, a horn having a pair of oppositely disposed, substantially parallel, conductive surfaces of substantially the same configuration, one of said surfaces being superimposed over the other of said surfaces so that the corresponding edges of said surfaces are adjacent, each of said surfaces having the configuration of a trapezoidal surface curved about its longitudinal axis, said curved trapezoidal surface originally having first and second edges perpendicular to, and symmetrical with respect to, said longitudinal axis, said first edge being substantially shorter than said second edge, the first edge of said curved trapezoidal surface being curved in the form of an arc of a circle, the mid point of said are being coincident with said longitudinal axis, the second edge of said curved trapezoidal surface being linear, the triangular area of said trapezoidal surface included between the linear edge and two lines extending from each end of said linear edge to the center of said curved first edge being substantially flat, the sides of the curved trapezoidal surface corresponding to the sides of the original trapezoidal surface being tapered in height with respect to said flat surface, the height of each of said sides being a maximum at said curved edge and zero at said linear edge, and a source of electromagnetic radiation adapted to be revolved so as to repeatedly traverse the space between said arcuately curved edges.

14. An antenna as in claim 13, said antenna further comprising means for receiving the energy emanating from between said linear edge and diverting said energy in a direction other than axially of said horn.

15. Apparatus as in claim 13 wherein the surfaces at said linear edges are further extended and bent so as to form a reverse bend for reversing the direction of propagation through said horn.

16. An antenna as in claim 13 wherein said second bases are further extended and bent so as to form conical parabolic reflecting surfaces, also uniformly spaced, whereby the circular wave front electromagnetic waves being propagated along said horn are transformed and radiated as a plane wave front beam in a direction other than axially of said horn.

17. Apparatus of claim 13 wherein the surfaces at said linear edges are further extended and bent so as to form a reverse bend for reversing the direction of propagation, said extended and bent surfaces also being equi-spaced, the spacing therebetween being the same as that between said first-mentioned pair of conductive surfaces, and adtion of propagation.

References Cited in the file of this patent UNITED STATES PATENTS Barrow Apr. 13, 1945 6 Hansen June 25, 1946 Mason Oct. 1, 1946 Beck Oct. 15, 1946 Iams June 8, 1948 Iams Apr. 18, 1950 Iams Oct. 3, 1950 

